This invention relates to the synthesis of alkylcyclopentadienes. More particularly the invention relates to the synthesis of tetramethylcyclopentadiene (TMCp).
U.S. Pat. Nos. 5,817,849 and 5,470,993 describe various metal complex addition polymerization catalysts and catalyst precursors which may be derived from TMCp.
Garner, Tetrahedron Letters (1994) 16:2463-2464 reports an overall 36% yield of TMCp from 2-butyne. Divinylcarbinol cyclodehydration to produce TMCp is described in U.S. Pat. No. 5,329,056.
Pursuant to the invention, 2-bromo-2-butene is produced in good yield by reaction of 2,3-dibromobutane with methanolic sodium hydroxide. Reaction of a Grignard derived from the 2-bromo-2-butene with ethyl formate yields 3,5-dimethyl-2,5-heptadiene-4-ol magnesium bromide, which is quenched with aqueous acetic acid to produce 3,5-dimethyl-2,5-heptadiene-4-ol (divinylcarbinol). TMCp for synthesis of addition polymerization catalysts is produced by cyclodehydration of divinyl alcohol with aqueous hydrochloric acid and ether, followed by caustic treatment to remove chlorotetramethylcyclopentene and sodium bromide.
Under appropriate conditions, an overall (distilled) TMCp yield of 50% to 75% from dibromobutane may be observed.